It is estimated today that, for all of the active oil reservoirs, 60%-65% of the oil in place remains trapped. Various mechanisms are responsible for this trapping, for example, geological heterogeneity generates non-homogeneous displacement of the oil at reservoir scale. However, even at local scale, the presence of an interfacial tension between water and oil leads to capillary trapping of the oil phase in the centre of the pores in the case of water-wet rocks. This trapping can represent up to 50% of the oil in place. Water-wet reservoirs constitute approximately half of the world's reservoirs.
Mobilizing the residual oil contained in the matrix under preferential water wettability conditions therefore is a real challenge. However, using surfactants injected in aqueous phase can lead to a significant capillary trapping decrease. Surfactants have the property of reducing considerably this tension or even of nearly cancelling it out. The use of surfactant additives has been successfully tested on sandstones in the 1980s and it is experiencing renewed interest. Surfactant enhanced oil (hydrocarbons) recovery methods represent a strong potential as they allow to untrap a significant amount of oil blocked in the pores of rocks.
To characterize capillary untrapping, it is necessary to perform measurements of relative fluid flow properties in the porous medium. Currently, the methods used require several weeks to obtain this fluid flow characterization. Indeed, it is currently necessary to prepare rock samples having a sufficient pore volume for the fluids produced and collected at the pore volume outlet to have a sufficient volume for characterizing the properties of the medium (typically several milliliters). Thus, typical sample sizes are of the order of 5 cm in diameter and 10 cm in length. The samples are then initially saturated with water, drained with oil and finally subjected to waterflooding so as to obtain the residual oil saturation. Injection of a volume of an ASP (Alkaline-Surfactant-Polymer) formulation and subsequently a final waterflooding sequence are then performed. At the end of the sequence, the residual oil saturation is deduced from the total volume of oil produced at the porous medium outlet.
Besides, in other technical fields, it may be interesting to rapidly characterize the flow of a fluid in a porous medium, notably a porous medium consisting of a polymer.
The invention relates to a system and to a method for measuring at least one flow property of at least one fluid in a porous medium. The measurement system comprises at least one cell, means for injecting fluid(s) into the cell and X-ray radiography means. Using X-ray radiography means in a cell into which a fluid can be injected allows measurements to be performed rapidly and in real time.